Leak testing is used to verify the integrity of a subject item under test. There are a variety of items that have been subjected to leak testing of one type or another. These items may be referred to generically as a “test part”.
Leak testing technology is used to verify whether or not the test part has a leak, and sometimes the amount of leaking involved. In some cases, leak testing may also be used to estimate generally where the leak is coming from. Production leak testing aims to identify leaking parts before they are shipped to a customer. Leak testing may also be practiced in the field, after the test part has already shipped and even possibly after the test part has been installed into a larger system (if the test part is a part of a larger system, rather than a stand alone piece).
There are a variety of leak tests conventionally available. Some of these test methods use air, and some use tracer gas. Some air-based testing methods include pressure decay testing, mass flow leak testing, bubble-immersion testing, and so forth. Tracer gas leak testing methods include a wide variety of methods. Two of these methods called helium atmospheric accumulation testing and helium hard vacuum testing will now be briefly summarized.
Helium atmospheric accumulation testing sometimes measures a leak flowing from a test part that is pressured with gas that includes tracer gas such as helium. If there were one or more leaks in the test part, helium (and perhaps other gases) would leak into the ambient environment. This testing method, however, provides a chamber or enclosure which, at least temporarily, captures all or some of the gases that leak from the test part. The helium levels may then be measured to infer the total leak rate for the test part.
In the helium hard vacuum test, helium gas is sealed inside a test part and a high vacuum is applied to the outside of the test part. Alternatively, helium gas is introduced to the outside of the test part, and the inside of the test part is evacuated to a high vacuum. In either case, a mass spectrometer in the hard vacuum side of the boundary then detects leakage across the boundary by detecting small amounts of helium gas present in the vacuum.